Maple sap

What I've learned about this is: Maple sap is exuded from the xylem, not
the phloem. It is the result of positive pressures generated in the stem.
Starch stored in the stem is hydrolyzed to sugar and moves from the xylem
parenchyma into the vessel elements. The latter seem not to have a callose
plugging mechanism.
Carl S. Pike (717) 291-3958
Department of Biology FAX (717) 399-4548
Franklin and Marshall College Internet C_PIKE at ACAD.FANDM.EDU
P.O. Box 3003
Lancaster, PA 17604-3003 USA